1. The Field of the Invention
The present invention relates generally to toner cartridges. More particularly, it concerns a method for increasing the printed page output and regulating the transfer rate of a certain amount of toner material in a toner cartridge as part of a printing process.
2. The Background Art.
Laser printers are known in the field of computer technology for reproducing the images of a computer screen as high quality printed images on a piece of paper. Electrostatic charge patterns corresponding to the images on the screen are produced on a rotational drum. These charge patterns are exposed to a magnetic roller coated with oppositely-charged toner particles. The toner particles are attracted from the roller to the charge patterns on the drum. The toner is thereby arranged in the image of the charge patterns, which correspond to the images on the computer screen. The toner on the drum is exposed to a piece of paper passing below the drum. A corona wire lies below the paper and carries the same charge as the charge patterns but at a much higher charge concentration. The toner particles are attracted to the corona wire and fall from the drum onto the paper in the arrangement of the charge patterns.
At this point, the toner sits loosely on the paper surface in an arrangement corresponding to the images on the computer screen. The paper is passed between upper and lower fusing rollers, the upper fusing roller being heated from within to a high temperature. The fusing rollers are pressed together as the paper passes therebetween, melting the toner particles and squeezing the melted toner into the fibers of the paper. The paper carrying the fused image exits the machine.
Toner material is typically made from ground particles of lead graphite. Toner is expensive and poses environmental concerns such as groundwater contamination, leaching of the soil, and so forth. It is therefore desirable to use toner in an efficient, productive manner and avoid toner waste which becomes released into the environment. However, the mechanics of extracting the toner from a toner supply and delivering it to a piece of paper involve many steps and machine parts, and necessarily cause toner waste which results in a reduced page yield and a less than perfect toner transfer rate. The term "page yield" as used herein refers to the average number of printed pages produced from a certain quantity of toner, typically one gram. The term "toner transfer rate" as used herein refers to the percentage of the toner which actually reaches the paper and gets used. Stray toner which is left on the drum surface is wiped off of the drum and delivered to a waste hopper. Hence, if seventy percent of the toner reaches the paper, then roughly thirty percent reaches the waste hopper and the toner transfer rate is seventy percent.
Of current interest are apparatus and methods for increasing the page yield and the toner transfer rate in a toner cartridge. It is known in the field to produce disposable/rechargeable toner cartridges having a self contained toner supply hopper, magnetic roller, drum, corona wire, and waste hopper. The toner cartridge is placed into a laser printer adjacent to fusing rollers therein to cooperate with the printer to carry out the printing functions described above. When the toner in the cartridge is used up, the cartridge is removed and either discarded or recharged.
Many attempts have been made to produce a toner cartridge which maximizes both the page yield and the toner transfer rate. However, the developers of the prior art toner cartridges have been unable to identify all of the key variables involved. The prior art toner cartridges have a number of disadvantages, and the developers thereof have generally attempted but failed to optimize the page yield and toner transfer rate. The page yield per gram of toner remains low, and the amount of toner waste delivered to the waste hopper remains high. The cost to end users is thus increased, and the negative effect on the environment of the wasted toner is multiplied.